Here are the code names for DirectX as far as I remember them.

• DirectX 1: Manhattan.
• DirectX 2: Orion.
• DirectX 3: Orange.
• DirectX 4: Mustard.
• DirectX 5: Diesel.¹
• DirectX 6: Kool-Aid.

Do you see the theme? I added some links to help you out, but try to guess the theme before clicking through.

Craig Eisler, one of the founding members of DirectX, has more history of DirectX on his (former) web site, including a picture of the first four project patches. I wrote that only to distract you so you would have to spend more time trying to guess what the theme was.

The names were typically brainstormed by the development and test teams in a conference room during one of our frequent “let’s order some pizza because we’re all working late” dinners. (I don’t remember anybody from management ever joining us for dinner.) People would throw out ideas, and the winner was determined by acclamation.

Okay, enough stalling. The theme was “weapons of mass destruction (with plausible deniability).” The plausible deniability was there so that if somebody asked us what the code name meant, we could make up something like, “Diesel, like the fuel. Because DirectX 5 is going to be even more powerful!”

• Manhattan: The Manhattan Project, the project to develop the atomic bomb.
• Orion: The Orion Project, using atomic bombs as a means of spaceship propulsion. (Yes, not a destructive use of atomic bombs, but similar in spirit.)
• Orange: Agent Orange, the horrific defoliant employed in Vietnam.
• Mustard: Mustard Gas, the deadly chemical weapon from World War I.
• Diesel: The Oklahoma City bombing employed what was reported as a mixture of ammonium nitrate and diesel fuel (really: nitromethane). One of the DirectX developers owned a farm and gave each team member a small plastic bag of ammonium nitrate as a souvenir.
• Kool-Aid: The Jonestown Massacre, wherein cult members drank a flavored drink (not actually Kool-Aid) as part of a mass suicide.

As you can see, this was the era when the DirectX team relied upon its reputation as a bunch of renegades.

Bonus chatter: I recall a team meeting at the start of the DirectX 6 project where management proudly unveiled the project code name, which I believe was Krakatoa. The development and test teams found this announcement amusing, because we had already set up the source code server and named it KOOLAID. Management could call it whatever they liked, but we already named it.

We also wondered why management thought to name a project after a volcano that famously self-destructed. But maybe they were trying to get onto the renegade bandwagon.

¹ I came up with the name Diesel. I believe this is the only time I ever contributed a product code name.